(a) Field of the Invention
This invention relates to mouldable compositions and moulded articles based on mineral aggregate and sulphur as well as to processes for their preparation; more especially the invention is concerned with sulphur concrete, sulphur mortar and other sulphur-bound composite materials of improved ductility and/or durability, particularly concretes and mortars wherein the aggregate contains a swelling clay.
(b) Description of the Prior Art
Mixtures of mineral aggregate and sulphur, wherein the sulphur functions as a binder are termed sulphur concretes or sulphur mortars depending on the form of the mineral aggregate.
Articles which may be formed by casting such sulphur concretes include preformed concrete articles conventionally formed from concretes based on a mixture of a hydraulic cement, such as Portland cement, mineral aggregate and water together with various additives. Such articles include paving slabs, structural members, curbing, gutters, pipes and other cast products.
Sulphur mortars may be employed, for example, in the cementing or joining of pipe, bricks and tile, and as coating compositions to provide a protective surface.
Sulphur concretes and mortars display certain advantages, as compared with Portland cement, although they also suffer from certain disadvantages. A particular advantage of the sulphur compositions (concretes and mortars) is that the solidified material can be re-used by heating it so as to re-melt the sulphur. This reduces waste since, for example, an imperfectly cast article can be melted down and recast.
Further sulphur is available in large quantities both as a by-product of oil refining and natural gas processing in the petroleum industry and from mining of sulphur deposits.
Concretes containing sulphur have been described in U.S. Pat. Nos. 3,954,480 and 4,025,352. In U.S. Pat. No. 3,954,480, Inderwick sought to provide concretes of improved strength and durability by employing powdered sulphur in admixture with Portland cement, water and mineral aggregate. In U.S. Pat. No. 4,025,352, Leutner et al sought to provide concretes having improved compressive strength and flexural strength, and improved corrosion characteristics by including dicyclopentadiene in the sulphur-aggregate mixture and controlling the interaction between the sulphur and the dicyclopentadiene.
Sulphur concretes and mortars tend to be very brittle, and there is very little reduction in stiffness as the ultimate load is approached so that failure occurs in the region of the maximum strength of the material. When such failure occurs, crack propagation is very rapid. This behaviour is very different to that of Portland cement, which shows significantly greater ductility.
The brittle nature or low ductility displayed by sulphur concretes and mortars represents a serious deficiency, particularly in comparison with the more conventionally used Portland cement, which has considerably delayed the acceptance of the materials commercially.
Various attempts have been made to improve the ductility of sulphur concretes by plasticizing the sulphur or changing it to a polymeric form. These attempts usually involve the addition of polymeric sulphides or substances which react with elemental sulphur to produce polysulphides in situ. The use of elemental arsenic and phosphorous to produce a rubbery material with sulphur is described in the Journal of Colloid Science, 17, (1962), page 717 by Tobolsky et al. The use of thiokols to plasticize sulphur has been described in The Bulletin of the American Ceramic Society, Vol. 16, No. 11, Nov. 1937, pages 435-438 by Dueker and Schofield and in Advances in Chemistry, Series 110 (Sulphur Research Trends) 1971, pages 201-207 by Dale J. M. The use of unsaturated organic compounds to plasticize sulphur has been described in Advances in Chemistry, Series 140 (New Uses of Sulphur), American Chemical Society, 1971, by Currel et al.
However, Currel et al also reported (see above) as did Blight et al in Advances in Chemistry, American Chemical Society, 1977 ("Preparation and Properties of Modified Sulphur Systems", Sulphur Utilization--A Progress Report), that unless large proportions of the modifier or plasticizer were employed, crystallization of the sulphur in the orthohombic form eventually occurs, with the loss of previous beneficial effects and restoration of the brittle state.
There is thus a need to provide ductile sulphur concretes and mortars, which do not revert to the brittle state.
A further problem with sulphur concretes and mortars exposed to the environment, occurs when the mineral aggregate contains a swelling clay, in that such concretes and mortars disintegrate rapidly when exposed to water or aqueous systems either by direct immersion in the water or by exposure to water in the atmosphere, for example, rain, humidity or melting snow. The problem occurs even with relatively minor amounts of swelling clay in the aggregate, for example, 1.0%, by volume.
Thus mineral aggregates containing swelling clay have either been avoided or careful pre-washing of the aggregate to remove the swelling clay has been necessary.
It would clearly be advantageous to be able to employ a mineral aggregate containing swelling clay, when such aggregate is readily available, for example, in regions where clay occurs naturally in the collected aggregate.
It is an object of this invention to provide sulphur concretes, mortars and coatings of improved ductility.
It is a different object of this invention to provide sulphur concretes, mortars and coatings which have good durability, particularly resistance to disintegration in water, and which employ an otherwise unusable mineral aggregate containing swelling clay.
It is a further object of the invention to provide sulphur concretes, mortars and coatings which have both ductility and durability, particularly resistance to disintegration in water.
It is a still further object of this invention to provide processes for the manufacture of such sulphur concretes, mortars and coatings.